The postnatal development of both the optical and neural visual systems is dependent on visual experience. Visual experience is defined by the information available in the retinal images in the two eyes. The goal of the proposed research is to extend our previous examination of retinal image quality in one eye during infancy to full binocular viewing conditions. We will examine human infants'visual experience in the context of image clarity and image alignment, which are primarily defined by accommodation and vergence responses and their interaction. These studies will document the emergence of the interaction between accommodation and vergence and their role in the development of refractive and accommodative strabismus. There are three specific aims: i) To understand the normal maturation of the relationship between accommodation and vergence with emmetropisation and growth of the distance between the eyes. ii) To determine the relative bias towards accommodation or vergence accuracy during the critical period of human development. iii) To understand the effects of accommodation and vergence behavior on visual experience of infants and children with high hyperopia or strabismus. PUBLIC HEALTH RELEVANCE: This project will determine how young infants and children manage apparently conflicting focusing and eye alignment demands during typical development. It will also investigate why some children develop refractive or accommodative strabismus while others, with apparently matching visual systems, do not. The goal is to develop intervention strategies to prevent this strabismus and associated amblyopia.